Problem
An advertising company wants to send a letter to all its clients announcing a new fee schedule. The clients' names are on several different lists in the company. The company merges the various lists to form one file, Client_Names, but obviously the company does not want to send the same letter twice to anyone. Write a program that removes any clients appearing in the file more than once. On each line of data there is a four-digit code number (with no leading zeros), followed by a blank, and then the client's name. For example, Amalgamated Steel is listed as:
Amalgamated Steel
Your program should create a new file that contains the same information (not necessarily in the same order) as the old file but without duplicates. Use an array indexed by four-digit code numbers in your solution.